1. Field of the Invention
This invention relates to the measurement of boreholes and underground caverns. More particularly, this invention relates to determining the configuration of a borehole by introducing an inert gas, such as nitrogen, into the borehole, and determining the weight of the nitrogen being introduced with the use of a flow meter apparatus, and monitoring the movement of the nitrogen gas interface down the borehole for determining the borehole configuration. Having determined the configuration of the borehole, any movement of the nitrogen interface upward or downward over a period of time indicates the relative location and amount of leakage that may be occurring from the storage cavern or wellhead area.
2. General Background
In the oil and gas industry, and in other related industries where there are storage caverns and the like within the earth for storing minerals such as oil, natural gas, sulphur, etc., these caverns, often being at a great depth beneath the surface of the earth, are reached through the use of boring a borehole from the surface of the earth down into the cavern. The borehole, of course, would accommodate the flow of minerals that are to be stored in the storage cavern both downward, and the movement of the minerals up through the borehole, of course, would accommodate the flow of minerals that are to be stored in the storage cavern both downward, and the movement of the minerals up through the borehole as the minerals are utilized. After a certain depth, these boreholes are simply holes drilled within the earth and have no pipe or casing to support the walls which may serve to prevent erosion or the like of the walls of the borehole. That being the case, in the preparation of the cavern by inserting salt water, or in the insertion of or the retrieval of the liquid minerals that are flowing through the borehole, the walls of the borehole become eroded, and the borehole itself may be in such a state that it is no longer effective in being used as a conduit for the passage of minerals and the like into the cavern.
Therefore, it is essential in the storage of such minerals and the preparation of the cavern, that the boreholes are carefully monitored in order to determine whether or not the borehole is in the proper shape that it is not so eroded that it is ineffective in its use. Likewise, often the configuration of the cavern itself is measured in order to determine the extent of erosion of the cavern. Also, following the determination of the configuration of the borehole, one may determine this in the process of the present invention, by the relative movement of the interface either upward or downward over a given period of time, whether or not there is leakage occurring in the cavern or at the casing seat, in order to ascertain that the borehole and cavern are in proper shape for storage of minerals or the like.
One known process for measuring the configuration of the borehole is to use an inert gas such as nitrogen gas and insert it down the hole. The pressure of the gas is measured as it leaves its source, and a measurement is attempted in order to determine how much gas is being used to fill a certain void within the borehole. What is utilized in the present state of the art is a measuring device which is marketed under the trademark of a "Barton Gauge" which records the number of inches of nitrogen being pumped out of the tank. This particular method falls very short of being in the least bit accurate, and is totally ineffective. At present, both governmental and industry requirements are such that the amount of inert gas being used to measure the configuration of the borehole must be within five pounds of the actual amount being pumped down the hole, and under the present method, this determination is ineffective.
There have been several patents which speak to the measurement of pressure, etc. either down the borehole or methods of determining the size of an orifice, the most pertinent being as follows:
U.S. Pat. No. 2,374,154 issued to C. B. Moore entitled "Comparator Gauge" teaches the use of a type of pneumatic guage for recording demensions of an internal bore at successive locations down the borehole. Essentially, the apparatus includes a transmitter head with a pressure transmitter within on the end of a flexible tube which is able to extend the length of the bore to be measured. It further provides an air compressor which supplies pressurized fluid to a receiver through the supply pipe to pressure regulators. The fluid supplied to the transmitter head is then delivered through the bore to the fluid pressure chamber. The apparatus then provides a readout of the pressurization within the bore which is then transmitted into a chart as the transmitter is moved down periodically the borehole. This apparatus in no way measures the configuration of the borehole due to the change in the weight of the measuring medium such as in this case, nitrogen.
U.S. Pat. No. 2,513,374 isued to C. Stead, et al entitled "Measuring Apparatus for Gauge Determination of Dimensions of Bodies with Flow of Fluid Under Pressure From an Orifice"[teaches the use of a measuring apparatus which has the capability of gauging dimensions of bodies by comparison with those of a master or standard, and determining the deviation from the "standard." The apparatus uses a Venturi means for providing differential fluid pressure for efficient operation of a gauge meter such as air and to permit bi-manual manipulation adjustment of a valve to 0 for comparatively measuring the dimensions of the body. In the claims of this particular patent, there is claimed a Venturi means as part of the combination for responding to the differential pressures and verifying the dimensions of the orifice being engaged.
U.S. Pat. No. 1,919,546 isssued to H. W. Fletcher entitled "Method and Apparatus for Testing Internal Diameter of Tubes" teaches the use of a device for testing the uniformity of the internal diameter of tubes so that inequalities within the internal walls of the tubes may be found. The invention is carried out by noting the amount of fluid that leaks past a cylinder of uniform diemater that moves within the tube. This is quite unlike the invention which relys on the interfacting of the layer of nitrogen with the atmosphere as it moves down the hole and conforms itself to the irregularities within the borehole. Please note also in the claims that there is claimed a gauge piston form to fit the tube loosely, and the other mechanisms which relate to this type of measurement.
U.S. Pat. No. 2,669,864 issued to O. C. Brewster entitled "pneumatic Bore Gauge" is basically an improvement patent upon pneumatic bore gauges of that time by having the ability to use a bore head to obtain the results of a two-range diameter of the hole. As with the other patent, what is required in this patent is an apparatus having a head which goes down the bore hole for determining the shape of the hole. And there appears to be no language in the patent which does teach the use of this particular apparatus down an oil well bore and is simply a patent on an improved bore head.
U.S. Pat. No. 4,000,655 issued to Jones entitled "Measuring Devices for Bores and Ducts" teaches the use of a means for measuring the irregularities on the inner surface of a pipeline by having a fluid filled envelope whereby the surface of the envelope would fill the irregularities of the hole. There would be a means for sensing the pressure variations within the envelope.
U.S. Pat. No. 3,456,504 issues to C. C. Bombardieri entitled "Sampling Method" teaches the use of a method for analyzing the subsurface formation by introducing two types of fluid at a selected ratio and analyzing the fluid following their injections into the formation.
U.S. Pat. No. 3,502,169 issued to J. E. Chapman, III entitled "Sonic Borehole Televiewer Apparatus" teaches the use of an electrical instrument for situating within a borehole and the apparatus responding to changes in the emissions within the hole and recording a record of the surface of the borehole wall.
U.S. Pat. No. 4,155,248 issued to Wagner, et al entitled "Method and Apparatus for Determining the Pressure Drop and Circumference of Filter Rods" teaches the use of a method for determining the circumference of and the pressure drop of filter rods for cigarette filters or the like.
U.S. Pat. No. 3,841,152 issued to Guest entitled "Drilling Conditions Monitor" teaches the use of a system which produces a digital readout for recording the pressure of the fluid circulating in the well bore and in doing so to detect a "kick" shortly after it occurs and take corrective action in order to prevent a blowout.
U.S. Pat. No. 3,172,129 issued to Rhoades entitled "Simplified Wellbore Pressure Testing Apparatus" for determining the bottom hole pressure in an oil well by use of a combination of instruments and recording the change in the pressure.
U.S. Pat. No. 4,250,947 issued to Heilhecker, et al entitled "Apparatus and Method for Detecting Abnormal Drilling Conditions" is done by monitoring mud volume of the mud system or the rate of change in the mud volume for detecting the abnormal conditions when the rate of makeup mud addition differs from the rate of solids removed from down the hole.